SQL stands for Structured Query Language. It is a domain-specific language used in programming and designed for managing data held in a relational database management system (RDBMS), or for stream processing in a relational data stream management system (RDSMS). It is particularly useful in handling structured data, i.e., data incorporating relations among entities and variables.
SQL consists of a data definition language, data manipulation language, and a data control language. The scope of SQL includes data insert, query, update and delete, schema creation and modification, and data access control. Here are some of the key elements of SQL:
Data Definition Language (DDL): This part of SQL allows you to define and modify the database schema, i.e., the structure of the data. It includes commands like CREATE, ALTER, and DROP which can be used to create and modify tables, views, indexes, and other database objects.
Data Manipulation Language (DML): This subset of SQL is used for data retrieval, insertion, deletion, and updating. The main commands are SELECT, INSERT, UPDATE, and DELETE.
Data Control Language (DCL): DCL includes commands such as GRANT and REVOKE which are used to manage rights and permissions for database users.
Transaction Control Language (TCL): TCL commands like COMMIT and ROLLBACK are used to manage transactions in the database. They allow you to handle the changes made by DML statements in a controlled way.
Some common SQL commands include:
SELECT: Retrieves data from one or more tables.INSERT INTO: Inserts new data into a table.UPDATE: Modifies existing data in a table.DELETE: Removes data from a table.CREATE TABLE: Creates a new table.ALTER TABLE: Modifies an existing table structure.DROP TABLE: Deletes a table from the database.CREATE INDEX: Creates an index (search key).DROP INDEX: Deletes an index.SQL is a standard language for relational database systems, and most database systems like MySQL, PostgreSQL, SQL Server, Oracle, and SQLite use SQL with their own proprietary extensions to the standard language for additional functionality. Learning SQL is essential for anyone who wants to work with databases because it allows for the querying and manipulation of data stored in an organized way.